This invention relates to an apparatus to be attached mainly to a hydraulic or pneumatic cylinder or the like which makes linear reciprocating movements, for detecting sliding displacements thereof.
To detect stroke displacements of a fluid pressure cylinder it has been general practice to use a limit switch, a proximity switch or a photoelectric switch which carries out detection through contact with or approach by a piston rod or a suitable element connected thereto. An on and off operation of the switch is transmitted through a control means to an electromagnetic valve mounted in a pressure fluid (i.e. oil or air) circuit to open and close the valve. This prior art construction has a problem that detection in a direct manner of stroke displacements makes it the more difficult to carry out a minute and precise detecting performance.
Under the circumstances, there has been a strong desire for a detecting apparatus which is attached, as if an adapter, to a newly maufactured or existing cylinder to detect its displacements with high precision. As an alternative to such an apparatus a cylinder has been desired which itself is provided with a construction to detect its strokes with high precision.
On the other hand, once a displacement is detected with precision as above, it is necessary to apply a reliable braking action to the piston or the cylinder. Known braking mechanisms generally have a construction as shown in FIG. 6. To describe the known construction particularly, a brake case comprising a brake tube 62 and covers 63 at respective ends thereof is provided forwardly of a rod cover 60 and coaxially with a piston rod 61. The brake case contains a rubber element 64 surrounding the piston rod 61 and a press plate 65 therefor. The piston rod is locked by the rubber element 64 when an actuating fluid under pressure is introduced through an inlet and outlet port 66 to expand the rubber element 64 toward its axis. A considerably high fluid pressure is required to effect a desired locking action, and a fluid pressure on the low side may result in an error in the braking position. Therefore, a braking apparatus has also been desired which acts in cooperation with a high precision displacement detector to apply a strong brake to a piston or a cylinder with small energy.